1. Field of the Invention
The present invention relates to a method of crystallizing amorphous silicon. More particularly, the present invention relates to a mask for laser irradiation using sequential lateral solidification, a method of manufacturing the same, and an apparatus for laser crystallization using the same.
2. Discussion of the Related Art
A sequential lateral solidification (SLS) method is used in a laser crystallization method, which is one method of crystallizing a silicon layer. The SLS method takes advantage of the fact that silicon grains grow laterally from the boundary between liquid phase silicon and solid phase silicon. A process crystallizing a silicon layer using the SLS method will be described hereinafter.
First, a first laser beam, which has an energy density completely melting the corresponding portion of a silicon layer, irradiates the silicon layer. The silicon layer exposed to the first laser beam is melted and then solidified. At this time, the first silicon grains grow laterally from the boundary between a liquid phase silicon region and a solid phase silicon region.
Next, the silicon layer is moved a distance, which is smaller than the silicon grain length formed by the shot of the first laser beam, and a second laser beam, which has the same energy density as the first laser beam, is irradiated on the silicon layer. The silicon layer exposed to the second laser beam is melted, and then second silicon grains grow in the same manner as with the first laser beam irradiation.
When the second silicon grains grow, the first silicon grains act as seeds of crystallization at the boundary between liquid phase silicon and solid phase silicon and grow laterally. Thus, the silicon grains grow in the direction that the laser beam moves.
As stated above, silicon grains having expected sizes are formed by repeatedly performing silicon crystallizing processes, where the silicon layer is moved, the laser beam is irradiated, and the silicon layer is melted and crystallized, n (n is a positive integer) times. The silicon grains grow laterally, i.e., in the scanning direction of the laser beam, from the first forming portion. Therefore, silicon grains of large sizes may be obtained.
The SLS method has a difference in the fact that the laser beam is patterned so as to have the fixed width and the fixed form from other laser crystallizing methods. To do this, an apparatus for a laser crystallization process using the SLS method uses a mask for patterning the laser beam differently from other conventional apparatuses for a laser crystallization process.
FIG. 1 is a schematic view illustrating an apparatus for a laser crystallization process using a SLS method. In FIG. 1, an apparatus for a laser crystallization process using a SLS method includes a laser beam source 10, an attenuator 11, a homogenizer 12, a field lens 13, a laser beam mask 14, an object lens 15 and a process chamber 20 having a translation stage 16. To irradiate a laser beam on a silicon thin film after patterning the laser beam in a fixed shape, an original laser beam naturally emitted from the laser beam source 10 is controlled passing through the attenuator 11, the homogenizer 12, and the field lens 13, and then is condensed. The condensed laser beam is patterned to have the fixed form through a beam pattern mask 14. The patterned laser beam passes through the object lens 15 and is irradiated on the silicon thin film 17 formed on the translation stage 16 in the process chamber 20. Because a silicon layer is generally formed on a substrate in a liquid crystal display device, the silicon layer and the substrate may be referred to all together as a silicon substrate. In FIG. 1, mirrors 19a, 19b and 19c control the path of the laser beam. The beam pattern mask 14 of the related art may be easily damaged, and thus the process yield may be reduced.